Hi Mahmoud,
1.Make sure master page/root you applied that default bootstrap css.
2.Make sure your page inherit master page template.
3.If you are using that tags in custom create user-control .ascx /.aspx pages then you must need to register it using below helper.
// Registers the default CSS
CssRegistration.RegisterBootstrap(Page);
4.If you want to render any other CSS on page
CssRegistration.RegisterCssLink(Page, "Default", "admin-common.css");
Thank
Happy to help you